The present invention relates to data storage devices and actuator control methods. More particularly, the invention relates to a data storage device and actuator control method for providing actuator control suited for retraction.
Various apparatus using optical disks, magnetic tapes and other types of media have been known as information recording and reproducing apparatus. Among them, the hard disk drive is popular as a storage device for computers so widely that it is one of the storage devices indispensable for today's computer systems. Further, not limited to computers, the hard disk drive is increasingly enlarging its area of application due to its superior characteristics including moving picture recording and reproducing apparatus and removable memories used in car navigation systems, digital cameras, etc.
A hard disk drive has a magnetic disk on which data is recorded, a spindle motor which rotates the magnetic disk, a magnetic head which reads/writes data to/from the magnetic disk and an actuator on which the magnetic head is fixed. Driven by a voice coil motor (VCM), the actuator is turned about a pivot to move the magnetic head. To read/write data, the actuator moves the magnetic head to the data zone on the surface of the rotating magnetic disk. The magnetic head has a recording/reproducing thin film element and a slider. Air between the rotating magnetic disk and the slider's ABS (Air Bearing Surface) facing the magnetic disk causes a pressure due to its viscosity. As a result of this pressure balanced with a pressure applied by the actuator toward the magnetic disk, the magnetic head flies above the magnetic disk with a certain gap therefrom.
When the magnetic disk ceases to rotate, the magnetic head is saved from the data zone in order to prevent the magnetic head from contacting the surface of the magnetic disk, which would cause flaws on the data zone or make it impossible to rotate the magnetic disk due to the adhering magnetic head. As a typical method for moving the magnetic head into the data zone on the disk and saving the magnetic head from the data zone, the ramp load approach is known. In the ramp load method, a ramp located near the magnetic disk is used to save the magnetic head. When the magnetic head is unloaded, the actuator is turned toward the ramp to rest the magnetic head thereon. During the unload, the actuator slides up an inclined surface of the ramp and reaches a flat parking surface of the ramp. During the load, the actuator kept on the parking surface slides down the inclined surface in the loading direction to leave the ramp and move to above the disk surface. The hard disk drive is also provided with an inner crash stop and outer crash stop which respectively define the innermost and outermost limits up to which the actuator can be turned over the magnetic disk. The outer crash stop prevents the magnetic head from passing through the ramp.
It is possible that power supply to the hard disk drive is interrupted while the magnetic head is above the rotating magnetic disk. Since the magnetic disk may have trouble as mentioned above if the magnetic disk contacts the magnetic disk, the magnetic head is saved to the ramp if the power supply is interrupted. While the power supply is ON, the actuator can be moved by controlling the VCM driver. If the power supply is interrupted, the magnetic head is unloaded to the ramp by a retract driver. A typical retract driver unloads the magnetic head by rectifying the back electromotive force of the spindle motor and supplying the rectified current to the VCM (Voice Coil Motor). In the case of a small hard disk drive not larger than 1.8 inches, however, it is usual that a voltage accumulated in a capacitor is utilized to drive the VCM since it is not possible to obtain a sufficiently large back electromotive force from the spindle motor.
To allow safer head retract control in such a hard disk drive provided with a retract driver, a technique is proposed which performs head retract control according to the head position when power supply to the driver is interrupted (see Japanese Patent Laid-open No. 2000-21073). In this hard disk drive, a switch is formed between the drive's general power supply line and a power supply line which supplies power to an unload control circuit including a CPU. If the interruption of the power supply is detected by a power supply interruption detecting circuit, the switch separates the power supply lines from each other so that a power supply voltage is applied to the unload control circuit from a capacitor connected to its power supply line. Normally, the CPU periodically determines a head retract control quantity as well as performing head control concurrently. If the interruption of the power supply is detected, the CPU gives the last determined control quantity to the VCM driver via a D/A converter, which drives the voice coil motor to retract the head to a predetermined retract position.